We propose to identify genes that underly susceptibility to asthma & atopy by performing two-point & complex linkage analysis with microsatellite markers in families with well-defined asthma. The study will focus on families with two affected siblings with asthma. Diagnosis of asthma in all family members will be made using strict criteria based on medical history and results of spirometry & methacholine challenge studies; skin tests for inhaled antigens will be performed & total IgE, specific IgE, & eosinophil counts will be measured.